Sergei Avdeyev (born 1 January 1956) is a Russian engineer and cosmonaut.

Avdeyev was born in Chapayevsk, Samara Oblast (formerly Kuybyshev Oblast), Russian SFSR. He graduated from Moscow Engineering Physics Institute in 1979 as an engineer-physicist [1]. From 1979 to 1987 he worked as an engineer for NPO Energiya. He was selected as a cosmonaut as part of the Energia Engineer Group 9 on 26 March 1987. His basic cosmonaut training was from December 1987 through to July 1989. He retired as a cosmonaut on 14 February 2003.